This invention relates to a cutting frame for use in a curd vat, which cutting frame comprises substantially parallel frame girders, between which is situated a lattice formed from longitudinal knives and transverse knives, of which the transverse knives have been mounted on the frame girders by welding and have aligned openings, in which the longitudinal knives are received and wherein means are provided for substantially preventing displacement of the longitudinal knives in the longitudinal direction.
The invention furthermore relates to a curd vat, also designated, for instance, as cheese vat, curd tank, curd container, cheese tank, etc., provided with one or more of such cutting frames. Such a curd vat may for instance be of a type as described in U.S. Pat. No. 4,108,058 or, for instance, of a type as marketed by Tetra Pak Tebel under the name of OST5. These known curd vats have a single rotatable shaft provided with a number of cutting frames mounted in staggered relation. The cutting frames according to the present invention, however, are also applicable in differently built-up curd vats, for instance curd vats with two shafts provided with cutting frames, as described, for instance, in U.S. Pat. No. 4,989,504. Further, the curd vats may be of the upright or lying type, whereby the shaft or shafts provided with cutting frames extends or extend substantially vertically and horizontally, respectively.
A cutting frame of the above-described kind and a curd vat provided with such cutting frames for cutting and stirring curd are known from European Patent 1084609.
All known apparatuses are arranged for stirring and cutting curd which has formed in the curd vat in that the vat has been filled with milk, to which starter and rennet have been added. To that end, depending on the type, one or more central shafts provided with cutting frames are driven for rotation, so that the cutting frames move through the curd formed. The cutting frames are usually so designed that the knives and the frame girders form a cutting edge along one edge and are blunt and rounded off along the other edge. Accordingly, rotation of the central shaft(s) in one direction yields substantially a cutting action, while rotation in the other direction yields substantially a stirring action.
A problem which occurs in older known apparatuses but which has been solved by the construction described in European Patent 1084609 is that the cutting frames in the older apparatuses comprise many welds, which must all be polished very well to prevent accumulation of contaminants and bacterial growth. The longitudinal knives can be arranged, for instance, with interspaces of the order of 4 to 5 cm and the transverse knives with interspaces of, for instance, 14.5 to 17.5 cm. A cutting frame can, for instance, have a total width of the order of 50 cm and a length of, for instance, 150 cm. This means that a single cutting frame can comprise, for instance, about 100 rectangular lattice openings, each having four corners, where a longitudinal knife or a frame girder is welded to a transverse knife. Each of those welds not only needs to be provided, but also needs to be accurately polished to satisfy the requirements set by government regulations regarding cleanability. For the welding operation, however, little space is available within the lattice openings formed by the longitudinal and transverse elements of a cutting frame. As a consequence, the welding work and the polishing work are very time consuming and costly.
According to the solution to the outlined problem described in European Patent 1084609, the longitudinal knives are situated in the openings of the transverse knives with ample play, while displacement of the longitudinal knives in the longitudinal direction is prevented by special means. These special means can for instance comprise a locking pin arranged through openings in the transverse knives and the frame girders, or, for instance, a small number of welds, preferably a single weld, for securing a longitudinal knife to a small number of transverse knives, preferably one transverse knife. In this way, the necessary welding and polishing work is considerably reduced and simplified, while yet an effective cutting and stirring action and a good cleanability remain guaranteed.
In practice, it has been found that in the course of time the cutting edge of the longitudinal knives can exhibit wear adjacent the openings of the transverse knives, as well as in a small area before and behind the transverse knives. This is due to the fact that during a stirring movement of the cutting frame, the cutting edge of the longitudinal knives, since the latter are situated in the openings in the transverse knives with ample play, is pushed against the edge of the openings, whereby moreover some torsion may occur in the longitudinal knives, which presumably worsens the wear referred to.